This invention relates to a liquid crystal display and, more particularly, to a method for producing an image on a liquid crystal panel, the liquid crystal panel and a liquid crystal display equipped with the liquid crystal panel.
A typical example of the liquid crystal display is shown in FIG. 1 of the drawings. The prior art liquid crystal display is broken down into a liquid crystal panel, a pair of polarizing plates 201/208 and a back light source 209. The liquid crystal panel is sandwiched between the polarizing plates 201 and 208, and light is radiated from the back light source 209 through the polarizing plate 208 to the liquid crystal panel.
The liquid crystal panel includes a pair of glass substrates 202 and 207 and liquid crystal 205 filling the gap between the glass substrates 202 and 207. Color filter elements 203R, 203G and 203B are arranged on the inner surface of the glass substrate 202, and the color filter elements 203R/203G/203B are covered with a common electrode 204. On the other hand, segment electrodes 206 are arrayed on the inner surface of the other glass substrate 207, and the segment electrodes 206 are aligned with the color filter elements 203R/203G/203B. The color filter elements 203R, 203G and 203B respectively transmit wavelengths recognized as red, wavelengths recognized as green and wavelengths recognized as blue therethrough, and a set of color filter elements 203R, 203G and 203B is associated with a pixel.
The color filters 203R/203G/203B and the common electrode 204 are formed on the inner surface of the glass substrate 202, and the segment electrodes 206 are formed on the inner surface of the other glass substrate 207. The glass substrates 201 and 207 are assembled together, and the liquid crystal 205 is injected into the gal between the glass substrates 202 and 207.
When a potential difference is applied between the common electrode 204 and selected segment electrodes 206, the liquid crystal changes the orientation of the liquid crystal molecules between the selected segment electrodes 206 and the color filter elements 203R/203G/203B. The back light source 209 radiates light toward the liquid crystal panel, and the liquid crystal molecules between the selected segment electrodes 206 and the common electrode 204 allow the light to pass therethrough. Thus, the light components are incident onto the color filter elements 203R/203G/203B. The color filter elements 203R/203G/203B absorb particular wavelengths of the incident light components, and transmits other wavelengths of the incident light components to the outside of the liquid crystal panel. The transmitted light components produce a color image on the liquid crystal panel.
A problem is encountered in the prior art liquid crystal display in a low transmittance of the light and a low production yield. The low transmittance is derived from the absorption of the incident light components. Each color filter element 203R/203G/203B absorbs two third of the incident light components, and only a third of the incident light components participates the production of the color image. The utilization factor of the Incident light is low. This is the first problem inherent in the prior art liquid crystal display. The low production yield is due to misalignment between the segment electrodes 206 and the color filter elements 203R/203G/203B. Even if the misalignment is not serious, the color image is not sharp.
The first problem may be solved by using a cholesteric filter disclosed in Japanese Patent Publication of Unexamined Application No. 8-234196. FIG. 2 illustrates the prior art cholesteric filter disclosed in the Japanese Patent Publication of Unexamined Application.
A light source 10 is encircled with a reflecting mirror 12, and a circularly polarizing plate 16 is provided between the light source 10 and the prior art cholesteric filter 18. The light source 10 generates the natural light, and the reflecting mirror 12 directs the natural light toward the circularly polarized plate 16. The light source 10, the reflecting mirror 12 and the circularly polarized plate 16 as a whole constitute a polarized light source. The polarized light source radiates circularly polarized light, which is polarized in a particular direction, toward the prior art cholesteric filter 18.
The prior art cholesteric filter 18 transmits the circularly polarized light of a particular waveband, but the circularly polarized light of the other waveband is reflected thereon. The prior art cholesteric filter 18 consists of two filter layers 20 and 22, and the filter layers 20/22 are divided into sections R, G and B. The sections R transmit wavelength components recognized as green and blue, and reflects the wavelength components recognized as red. The sections G transmit wavelength components recognized as red and blue, and reflect other the wavelength components recognized as green. The sections B transmit wavelength components recognized as red and green, and reflect the other wavelength components recognized as blue. The sections R/G/B of the filter layer 20 are offset from the sections R/G/B of the other filter layer 22. If the section B is overlapped with the section R, the part of the cholesteric filter 18 transmits the wavelength components recognized as green. Similarly, the wavelength components recognized as blue pass the section R overlapped with the section G, and the wavelength components recognized as red pass the section G overlapped with the section B. Two third of the incident light is previously reflected toward the circularly polarized light source, and is reused. For this reason, the utilization factor is increased.
When the cholesteric filter 18 is applied to a liquid crystal display, the cholesteric filter is inserted between the substrates. Noise component of the transmitted light component is absorbed by using a color filter.
However, the second problem is also encountered in a liquid crystal display equipped with the prior art cholesteric filter due to the misalignment between the pixels, the sections R/G/B of the cholesteric filter and the color filter during the assembling work. Even if the misalignment is not serious, the color image is not sharp.
It is therefore an important object of the present invention to provide a method for producing a clear color image on a liquid crystal display.
It is also an important object of the present invention to provide a liquid crystal panel, which is fabricated at a high yield.
It is also an important object of the present invention to provide a liquid crystal display, which is equipped with the liquid crystal panel for producing a sharp color image through the method.
To accomplish the object, the present invention proposes to recycle circularly polarized light components reflected on a cholesteric filter.
In accordance with one aspect of the present invention, there is provided a method for producing a visual image on a liquid crystal display comprising the steps of radiating an incident light, selecting one of the right-handed circularly polarized light component and the left-handed circularly polarized light component of a waveband from the incident light so as to recycle the other of the right-handed circularly polarized light component and the left-handed circularly polarized light component of the waveband and other light components of other wavebands of the incident light as a part of the incident light, converting the aforesaid one of the right-handed circularly polarized light component and the left-handed circularly polarized light component to a linearly polarized light component, removing a noise component of the other wavebands from the linearly polarized light component, if any, and producing a visual image from the linearly polarized light component by changing an orientation of liquid crystal molecules forming a part of an electric shutter.
In accordance with another aspect of the present invention, there is provided a liquid crystal panel comprising transparent substrates having respective inner surfaces opposed to each other by a gap, an electric shutter provided in the gap and including plural segment electrodes, a common electrode opposed to the plural segment electrodes and plural pieces of liquid crystal filling a gap between the plural segment electrodes and the common electrode so as to selectively changing orientations of the plural pieces of liquid crystal depending upon potential differences between the plural segment electrodes and the common electrode, and a spectroscope including a cholesteric filter formed over one of the transparent substrates for transmitting one of the right-handed circularly polarized light component and the left-handed circularly polarized light component of a waveband incorporated in an incident light toward the electric shutter and reflecting the other of the right-handed circularly polarized light component and the left-handed circularly polarized light component of the waveband and other light components of other wavebands incorporated in the incident light in the opposite direction to that of the aforesaid one of the right-handed circularly polarized light component and the left-handed circularly polarized light component of said waveband, a converter formed on a surface of the cholesteric filter on the opposite side to the aforesaid one of the transparent substrates for converting the aforesaid one of the right-handed circularly polarized light component and the left-handed circularly polarized light component to the linearly polarized light component of the waveband and a filter formed on a surface of the converter on the opposite side to the cholesteric filter for eliminating a noise component of the other wavebands from the linearly polarized light component.
In accordance with yet another aspect of the present invention, there is provided a liquid crystal display for producing a visual image comprising a liquid crystal panel including transparent substrates having respective inner surfaces opposed to each other by a gap, an electric shutter provided in the gap and including plural segment electrodes, a common electrode opposed to the plural segment electrodes and plural pieces of liquid crystal filling a gap between the plural segment electrodes and the common electrode so as to selectively changing orientations of the plural pieces of liquid crystal depending upon potential differences between the plural segment electrodes and the common electrode, thereby producing a visual image and a spectroscope including a cholesteric filter formed over one of the transparent substrates for transmitting one of the right-handed circularly polarized light component and the left-handed circularly polarized light component of a waveband incorporated in an incident light toward the electric shutter and reflecting the other of the right-handed circularly polarized light component and the left-handed circularly polarized light component of the waveband and other light components of other wavebands incorporated in the incident light, a converter formed on a surface of the cholesteric filter on the opposite side to the aforesaid one of the transparent substrates for converting the aforesaid one of the right-handed circularly polarized light component and the left-handed circularly polarized light component to the linearly polarized light component of the waveband and a filter formed on a surface of the converter on the opposite side to the cholesteric filter for eliminating a noise component of the other wavebands from the linearly polarized light component, and a light source radiating the incident light containing the other of the right-handed circularly polarized light component and the left-handed circularly polarized light component of the waveband and other light components of other wavebands toward the liquid crystal panel.